Implement gdbstub

1 files changed, 134 insertions, 0 deletions

diff --git a/sim/gdbstub.py b/sim/gdbstub.py
new file mode 100644
index 0000000..b262971
--- /dev/null
+++ b/sim/gdbstub.py
@@ -0,0 +1,134 @@
+import sys, socket
+
+start_halted = True
+
+def init():
+    global client
+
+    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+    sock.bind(('127.0.0.1', 1234))
+    sock.listen()
+    print('Listening for gdb on', sock.getsockname(), file=sys.stderr)
+
+    client, peer = sock.accept()
+    sock.close()
+    print('Accepted connection from', peer, file=sys.stderr)
+
+buffer = b''
+haltFromStop = False
+
+def halt():
+    global buffer, haltFromStop
+
+    if haltFromStop:
+        reply(b'S05')
+        haltFromStop = False
+
+    while True:
+        data = client.recv(4096)
+        if not data:
+            break
+
+        buffer = buffer + data if buffer else data
+
+        try:
+            start = buffer.index(b'$')
+            marker = buffer.index(b'#', start + 1)
+        except ValueError:
+            continue
+
+        if marker + 2 >= len(buffer):
+            continue
+
+        data = buffer[start + 1:marker]
+        cksum = int(buffer[marker + 1:marker + 3], 16)
+
+        if cksum != (sum(data) & 0xff):
+            raise Exception(f'bad packet checksum: {buffer[start:marker + 3]}')
+
+        buffer = buffer[marker + 3:]
+
+        client.send(b'+')
+
+        if data[0] == b'?'[0]:
+            out = b'S05'
+        elif data[0] == b'c'[0]:
+            assert not data[1:] #TODO
+            break
+        elif data[0] == b'D'[0]:
+            out = b'OK'
+        elif data[0] == b'g'[0]:
+            out = hexout(read_reg(gdb_reg(r)) for r in range(16))
+        elif data[0] == b'm'[0]:
+            addr, length = (int(x, 16) for x in data[1:].split(b','))
+            out = hexout(read_mem(addr, length))
+        elif data[0] == b'M'[0]:
+            addrlen, data = data[1:].split(b':')
+            addr, length = (int(x, 16) for x in addrlen.split(b','))
+
+            data = bytes.fromhex(str(data, 'ascii'))
+            assert len(data) == length
+
+            write_mem(addr, data)
+            out = b'OK'
+        elif data[0] == b'p'[0]:
+            reg = gdb_reg(int(data[1:], 16))
+            out = hexout(read_reg(reg) if reg is not None else None)
+        else:
+            print('unhandled packet:', data)
+            out = b''
+
+        reply(out)
+
+    haltFromStop = True
+
+def reply(out):
+    client.send(b'$' + out + b'#' + hexout(sum(out) & 0xff, 1))
+
+def gdb_reg(n):
+    if 0 <= n < 8:
+        return (r0, r1, r2, r3, r4, r5, r6, r7)[n]
+
+    if n == 15:
+        return pc
+
+    if n == 0x19:
+        return cpsr
+
+    mode = read_reg(cpsr) & 0b11111
+    if 8 <= n < 13:
+        if mode == 0b10001:
+            regs = (r8_fiq, r9_fiq, r10_fiq, r11_fiq, r12_fiq)
+        else:
+            regs = (r8_fiq, r9_fiq, r10_fiq, r11_fiq, r12_fiq)
+
+        return regs[n - 8]
+
+    if 13 <= n < 15:
+        if mode == 0b10011:
+            regs = (r13_svc, r14_svc)
+        if mode == 0b10111:
+            regs = (r13_abt, r14_abt)
+        if mode == 0b11011:
+            regs = (r13_und, r14_und)
+        if mode == 0b10010:
+            regs = (r13_irq, r14_irq)
+        if mode == 0b10001:
+            regs = (r13_fiq, r14_fiq)
+        else:
+            regs = (r13_usr, r14_usr)
+
+        return regs[n - 13]
+
+    return None
+
+def hexout(data, size=4):
+    if data is None:
+        return b''
+    elif type(data) is bytes:
+        return data.hex().encode('ascii')
+    elif type(data) is int:
+        data = [data]
+
+    return b''.join(hex(d)[2:].zfill(2 * size)[:2 * size].encode('ascii') for d in data)
+